JVC UX-A70MD - trouble detecting disc presence

[IC.]

Hello everyone, I'm here for the first time so I apologize if I'm using the forum incorrectly, I know it's a Sony forum, but it's the only Minidisc-related forum I could find that isn't on reddit.

I've recently gotten a used JVC UX-A70MDR mini system, as it turned out the MD and CD aren't really functioning properly.
At this point I have a lot of experience repairing electronics, I adore playing around with old hi-fi equipment, so I'm not really a beginner to this, but the problem here seems so stupidly simple yet so hard to diagnose that I've decided to try asking for help/advice.

The problem:
The mechanism is unable to detect whether a disc is present or not, after it has been already correctly loaded with the slot-loading mechanism which operates completely fine.
So, when it loads the disc, it just ejects it back out after a few seconds.

However, if I place the mechanism vertically on its left side, it somehow detects a loaded disc with almost 100% success rate. It spins it up, reads the TOC, and starts playing the audio just fine. Even if I place the mechanism back on its bottom in its correct horizontal orientation, it continues playing just fine without a single interruption. Playback works fully as intended. Skipping tracks and everything works just like it should.
But when I stop the playback (via the stop button or by switching to another audio source), the disc spins down. When trying to play the loaded disc again, it does not spin up, the laser/magnet head assembly only moves a little forward and back, and the mini system's interface goes back to the track listing instead of playing the disc.

So I am almost fully certain that the problem is with the detection of presence of a disc in the loaded position. If I rotate the mechanism to the side again when it tries to "detect" the presence of a loaded disc when wanting to play an already loaded disc, it once again spins up just fine and starts playing, which continues without any problem after placing the mechanism back on its bottom.


The service manual for this device is available online (I won't post links or pictures due to potential copyright issues), although it didn't help me much. There are apparently some switches under the "cam gear", but I don't think those are responsible for anything besides the slot-loading mechanism. I am honestly not sure if this "detection" of the disc is done by some physical switch, or if it's being done by the laser. But I'm leaning towards it being an issue with the laser, which would be weird since it works completely fine after it detects a disc, but at this point it seems the most logical that the detection of the disc is done by the laser, since I know that's how common CD readers detect the presence of a disc, and I can't locate any physical switch that would be responsible for that.


I'd appreciate if any of you Minidisc fans here have any idea, advice, or experience with an issue like this. However, I also fully understand that you probably don't have the time to look through a random service manual for some person on the Internet that you've never met before, just to see if you find anything they missed or didn't understand. Even if no one responds, at least some others with the same model might find this thread in the future and see that I had this issue and behavior.

If it's needed, I can take some photos of the mechanism and upload them here. I'm not sure if I'm allowed to post attachments as a new user.

Thank you!

 

TL;DR summary: JVC slot loading MD drive fails to detect the presence of a disc in the loaded position, which is being done after loading the disc but also when wanting to play it again after the disc has been stopped. If I rotate the mechanism onto its side, the disc detection somehow works just fine, and after the disc spins up, the entire mechanism continues to work just fine even after placing it back on its bottom.

[Syrius]

Having watched a repair video by a Youtuber, I can almost 100% assure you the detection is done by a micro-switch or some other physical sensor in the unit that gets pressed down when an MD is loaded.

 

This is the video in question, probably won't help you much, but it's the best reference I got:
 

 

 

Good luck.

[IC.]

I've seen that video a while in the past, but I will give it another watch once I return from work. Not sure if this will help me at all with this specific mechanism, though. I've tried really hard to locate a physical switch that could be responsible for the detection, both by disassembling the mechanism and studying the service manual, but found nothing. If it's a physical switch, it'd also be weird that the controller only checks its state once before reading the disc.

 

Trivia: Sony MDS-JE510 is a device I own too, but mine thankfully doesn't have this infamous issue of these Sony models, so I never even had to take it apart.

 

Thanks for the suggestion.

[BearBoy]

Hi @IC.. Welcome to the forum!

 

I'm not familiar with your JVC unit but does the loading mechanism use a belt? I've had an issue with Sony decks ejecting discs after a few seconds that's been solved by replacing the belt with a new one

[BearBoy]

Oh, and don't worry about posting about non-Sony kit. Despite the name, the forum's good for all things MiniDisc 🙂

[IC.]

Hi, yes, the loading mechanism does have a tiny belt for the motor, and I initially suspected the loading mechanism to be the issue, but the belt and auto-loading mechanism are both completely fine. It pulls the disc in forward and down completely fine to the end. I also have been applying a small DC voltage to the motor directly while I have the mechanism disassembled and outside of the unit, it works completely fine without any resistance.

 

I'm fairly sure it's not the loading mechanism, since when I do the trick with placing the drive on its side in order for it to detect and play the disc, but then stop the playback which makes the disc stop spinning, and then try to play the already loaded disc again, it fails to detect and spin up the disc unless I do the trick again. The loading mechanism does not move at all in the meantime, the disc stays in the fully loaded position.

 

This might really be a one of a kind of an issue, since I haven't been able to find anything about specifically such an issue online, when I was searching before posting on this forum.